# Fluid dynamics in ambient air pressure

There is a 100 ml bottle filled 80 percent with water. The lid is airtight. Two small 3.5ml tubes penetrate the lid without gap. One tube reaches almost to the bottom of the bottle, the other just a cm below the lid. Both tubes are clamped on the outside. The lid with the tubes is inserted into the 80% filled bottle. And the lid closed airtight. When the bottle is turned upside down I would expect that no fluid escapes from either tube. The tube that goes to the bottom of the bottle is ending in the airspace at the bottom of the upside down turned bottle. The other tube should not drain fluid as it should only be doing so if an equal amount of air goes into the bottle. However it appears that the short tube leaks a small amount of fluid before it stops. I guess the airspace inside the tube from the clamp on the long tube to its end at the bottom of the bottle adds extra air volume which allows an equal amount of fluid to enter the draining tube?

I suspect you are hoping for a bit more than "Yes, you are right".

First, the air in the long tube is compressed slightly as you put it into the water. The compressed air in the tube supports any water in the bottle above the level the water goes up the tube.

You then seal the bottle with the top air space at atmospheric pressure.

When you invert the bottle the air in the long tube expands while the weight of the water in the bottle compresses the air in the short tube.

A smaller air volume in the short tube means some water.

• Thank you I figured this by the time I asked the question. But thank you for your reply!
– Eule
Dec 5 '19 at 16:32